Articles with one or more structured surfaces find a variety of uses. The articles may be provided as films that exhibit, e.g., increased surface area, structures used to provide a mechanical fastener, optical properties, etc. When these films are manufactured for use as mechanical fasteners, the protrusions that are found on the structured surface are commonly referred to as hooks. The hooks may be formed in a curved shape or they may be substantially upright stems that are deformed in a subsequent operation to include, e.g., a head in the shape of mushroom.
Mechanical fasteners are sometimes designed so that two hook strips can be used to fasten two articles together by adhering each strip to one of the articles and then interengaging the two strips. Such a mechanical fastener is shown in U.S. Pat. No. 3,192,589 (Pearson) which calls the fastener “hermaphroditic” because its headed studs have both male and female characteristics when intermeshed. The Pearson fasteners can be made by molding a base from which integral headless studs project and then heat softening the tips of the studs.
U.S. Pat. No. 5,077,870 (Melbye et al.) discloses one method of manufacturing the hook strip portion of a mechanical fastener by forcing molten material into cavities formed in a moving mold surface. The stems formed by the moving mold surface are then capped to form the desired fasteners. The cavities are formed in the mold surface by drilling. As a result, the cavities are cylindrical in shape and, although some precision can be obtained in depth, diameter and spacing between cavities, it is obtained with some difficulty and increased costs. Furthermore, damage to the mold surface typically requires that the entire mold be discarded.
U.S. Pat. No. 5,792,411 (Morris et al.) discloses a molding tool manufactured by laser machining a mold surface. Molten material is then forced into the cavities in the moving mold surface to form stems. The stems are then capped to form the desired fasteners. Because the cavities are formed by laser ablation, the cavity shape is based on the energy distribution within the laser beam used to form the cavities. Furthermore, precise control over the depth of the cavities is difficult to obtain due to variability in the material used to construct the mold, the power of the laser beam, the energy distribution within the beam, beam focus, etc.
U.S. Pat. No. 4,775,310 (Fischer) and PCT Publication No. WO 97/46129 (Lacey et al.) disclose tooling used to manufacture hook strips for a hook-and-loop style mechanical fastener. The tools are formed by a hollow drum with a water cooling jacket. A series of mold disks or alternating mold disks and spacer plates are laminated together along the length of the drum to form the desired mold cavities on the face of the roll. Disadvantages of these designs include the cost of manufacturing the mold disks with adequate precision to ensure that the mold cavities are of the same depth, length, spacing, etc. Size limitations imposed on the disks by manufacturing difficulties can, in turn, limit line speed in processes using the tools. Other disadvantages of this design include non-uniform cooling of the mold cavities, non-uniformities in the products produced by the stacked plates, etc.